Cluster communication system realized based on 4G wireless network

Abstract

The invention discloses a cluster communication system realized based on a 4G wireless network, relates to the technical field of cluster communication, and is used for starting equipment, selecting an architecture for connection, monitoring a group calling signal of a group corresponding to group information in real time, sending the group calling signal to a terminal starting module, and starting the terminal starting module. After receiving the group calling signal, the terminal starting module sends the group calling signal to all online devices in a group, compresses voice data and transmits the voice data based on a PoC protocol, and the online devices monitor a multicast address in real time, obtain a call ending signal, send the call ending signal to the online devices and stop voice data transmission; through the multi-network fusion technology, seamless switching between the private network and the public network is achieved, the reliability and stability of communication are improved, trunking communication is carried out through the PoC protocol and the 4G / 5G network, the communication efficiency is improved, meanwhile, the communication cost is reduced through the optimized network transmission protocol, and the system has remarkable advantages in the fields of emergency communication and public safety.

Description

Technical Field

[0001] The present invention relates to the technical field of cluster communication, and in particular to a cluster communication system implemented based on a 4G wireless network. Background Art

[0002] The trunking communication system is a dedicated wireless communication system for specific industry applications. It has a wide range of application markets in government departments, public safety, emergency communications, rail transit, civil aviation and other fields. With the development of digital technology, the trunking communication system has gradually developed into a digital trunking communication system. The digital trunking system has the advantages of high spectrum utilization, strong signal resistance to channel fading, and good confidentiality.

[0003] At present, a Chinese invention patent with application number CN202211312097.0 discloses a group call method, a group call device and a cluster communication system, in which a first repeater receives business voice data sent by a first terminal and / or a second repeater; obtains superimposed voice data based on the business voice data received within a preset time interval, and sends the superimposed voice data to the first terminal so that the first terminal outputs the superimposed voice data; sends the superimposed voice data to the second repeater so that the second repeater sends the superimposed voice data to the second terminal, and the second terminal outputs the superimposed voice data.

[0004] The above technologies make it difficult to switch to other networks and reduce broadband usage when the signal is insufficient, affecting communication efficiency and communication costs. Summary of the invention

[0005] The technical problem solved by the present invention is that it is difficult for the above technology to switch to other networks and reduce the usage of broadband when the signal is insufficient, which affects the communication efficiency and communication cost.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A cluster communication system based on a 4G wireless network includes a terminal start module, a group call initiation module, a voice transmission module and a voice end module;

[0008] The terminal startup module is used to start the device and select the architecture for connection, output the first architecture data, collect the user identity information and group information input by the user and perform identity authentication, and monitor the group call signal of the group corresponding to the group information in real time;

[0009] The group call initiation module is used to send a group call signal to the terminal start module, establish a channel control mechanism, and select a connection architecture according to the channel control mechanism. After receiving the group call signal, the terminal start module sends the group call signal to all online devices in the group to obtain voice data;

[0010] The voice transmission module is used to compress the voice data, the voice data is marked with a multicast address, the voice data is transmitted based on the PoC protocol, the online device monitors the multicast address in real time, and plays the voice data corresponding to the multicast address after receiving it;

[0011] The voice ending module is used to obtain a call ending signal, send the call ending signal to an online device, stop voice data transmission, release the architecture corresponding to the first architecture data, and end the group call.

[0012] Preferably, the terminal startup module includes an architecture connection unit, an identity authentication unit and a group joining unit;

[0013] The architecture connection unit is used to start the device and set the architecture priority. The architecture priority is to connect to the private network first and obtain the private network signal. If the private network signal is less than the preset private network signal strength threshold, the public network is connected and the connected architecture is output as the first architecture data.

[0014] Preferably, the architecture connection unit is provided with an architecture switching time interval, and the time interval is a first time interval, and the private network signal is detected and the architecture switching is performed based on the first time interval.

[0015] Preferably, the identity authentication unit is used to collect identity information and group information input by the user, the identity information includes a user account, a walkie-talkie serial number and an integrated circuit card identification code, and input the identity information and group information into a user information database for verification. If the identity information and group information are located in the user information database, the verification is successful; if the identity information and group information are not located in the user information database, the verification fails and a verification failure signal is sent to the user end;

[0016] The group joining unit is used to monitor the group call signal of the group corresponding to the group information in real time.

[0017] Preferably, the group call initiating module includes a request sending unit, a resource allocation unit and a group call confirmation unit;

[0018] The request sending unit is used to obtain the group call signal of the group call terminal and send it to the terminal starting module;

[0019] The resource allocation unit is used to establish a channel control mechanism, and the channel control mechanism is:

[0020] If the first architecture data is a private network, selecting a private network base station as a resource allocation channel;

[0021] If the first architecture data is a public network, a dynamic multicast address pool is created on the PoC server, wherein the multicast address pool includes a plurality of multicast addresses, and a unique multicast address is allocated to each online device in the group;

[0022] The group call confirmation unit is used to receive a group call signal, and when receiving the group call signal, sends the group call signal to all online devices in the group to obtain voice data.

[0023] Preferably, the resource allocation unit is provided with a heartbeat detection mechanism, and the heartbeat detection mechanism is:

[0024] If the online device has no voice data transmission within the preset second time interval, the multicast address corresponding to the online device is automatically released, and the released multicast address is returned to the multicast address pool.

[0025] Preferably, the voice transmission module includes a multicast unit and a voice stream receiving unit;

[0026] The multicast unit is used to compress the voice data into Opus code and pack it into RTP data packets, wherein the RTP data packets are marked with a multicast address, and the voice data is transmitted based on the PoC protocol;

[0027] The voice stream receiving unit is used to start the online device to monitor the multicast address in real time, receive the voice data in the RTP data packet corresponding to the multicast address and play it.

[0028] Preferably, the logic of transmission in the multicast unit is:

[0029] If the first architecture data is a private network, the RTP data packet is transmitted through the physical channel of the private network;

[0030] If the first architecture data is a public network, the RTP data packet is transmitted in the form of a multicast stream through the multicast address of the 4G / 5G IP multicast network.

[0031] Preferably, the voice termination module includes a call termination unit and an architecture release unit;

[0032] The call end unit is used to obtain a call end signal from the group call end, and the dispatch server sends the call end signal to the online device to stop voice data transmission;

[0033] The architecture release unit is used to obtain the first architecture data and release it. The logic of the release is:

[0034] If the first architecture data is a private network, releasing the physical channel;

[0035] If the first architecture data is a public network, the multicast address of the 4G / 5G IP multicast network is released and the PoC multicast session is closed;

[0036] The group call is terminated after the architecture corresponding to the first architecture data is released.

[0037] Preferably, the public network transmission of the multicast unit caches the RTP data packets and uses forward error correction and retransmission mechanism.

[0038] Beneficial effects of the invention: The invention realizes seamless switching between private networks and public networks through multi-network integration technology, improves the reliability and stability of communication, adopts the PoC protocol, and uses 4G / 5G networks for cluster communication, thereby improving communication efficiency. At the same time, the optimized network transmission protocol reduces communication costs, and has significant advantages in the fields of emergency communications and public safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A basic flow chart of a cluster communication system implemented based on a 4G wireless network is provided for one embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, but not all of the embodiments.

[0041] Reference Figure 1 , which is an embodiment of the present invention, provides a cluster communication system based on a 4G wireless network, including a terminal start module, a group call initiation module, a voice transmission module and a voice end module.

[0042] The terminal startup module is used to start the device and select the architecture for connection, output the first architecture data, collect the user identity information and group information input by the user and perform identity authentication, and monitor the group call signal of the group corresponding to the group information in real time.

[0043] The group call initiation module is used to send a group call signal to the terminal start module, establish a channel control mechanism, and select a connection architecture according to the channel control mechanism. After receiving the group call signal, the terminal start module sends the group call signal to all online devices in the group to obtain voice data.

[0044] The voice transmission module is used to compress the voice data, which is marked with a multicast address. The voice data is transmitted based on the PoC protocol. The online device monitors the multicast address in real time and plays the voice data corresponding to the multicast address after receiving it.

[0045] The voice ending module is used to obtain a call ending signal, send the call ending signal to an online device, stop voice data transmission, release the architecture corresponding to the first architecture data, and end the group call.

[0046] The terminal startup module includes an architecture connection unit, an identity authentication unit and a group joining unit.

[0047] The architecture connection unit is used to start the device and set the architecture priority. The architecture priority is to connect to the private network first and obtain the private network signal. If the private network signal is less than the preset private network signal strength threshold, the public network is connected and the connected architecture is output as the first architecture data.

[0048] The architecture connection unit is provided with an architecture switching time interval, which is a first time interval. The private network signal is detected based on the first time interval and the architecture switching is performed.

[0049] The hybrid network of the architecture connection unit combines the advantages of private networks and public networks, and uses the high security of private networks and the wide coverage of public networks to switch between different communication environments. The private network, that is, a dedicated wireless network, communicates through dedicated base stations and physical channels, and has high security, low latency and strong anti-interference capabilities, but limited coverage. The public network is based on 4G / 5G cellular networks and communicates through IP networks. The IP network here is a PoC server in the present invention, which has a wide coverage and low cost, but in high concurrency conditions, network congestion and delays may occur. The hybrid network ensures priority connection to the private network and improves security. When the device starts, it tries to connect to the private network and switches to the public network when the signal is weak. It monitors the signal strength in real time and supports dynamic switching to ensure uninterrupted communication.

[0050] In addition, an algorithm can be designed to evaluate the quality of private and public network signals in real time and dynamically select the best connection architecture. The logic of the algorithm is:

[0051] Collect signal strength data, user network environment and server load, conduct signaling process tests and test enterprise applications and data channels, and evaluate the response delay, network delay, packet loss rate, jitter and network bandwidth of enterprise applications and data channels.

[0052] The signal strength data is preprocessed by the PLE algorithm, and then the Kalman filter is used to estimate the position and speed of the processed signal strength data. The PLE algorithm performs a power transformation on the received signal strength data to convert the nonlinear relationship into a linear relationship. The formula is:

[0053] Y=X α

[0054] Among them, X is the signal strength data, Y is the signal strength data after PLE processing, and α is the parameter of the PLE algorithm.

[0055] The technology automatically selects the best server for domain name resolution based on the user's network environment and server load. Intelligent DNS monitors the response delay, network delay, packet loss rate, jitter and network bandwidth of each server in real time, and selects the best server for domain name resolution based on the analysis results.

[0056] The architecture connection unit initializes the device and prepares for network connection. According to the preset architecture priority, it tries to connect to the private network, obtains the private network signal strength, and compares it with the preset threshold. If the private network signal is weak, it automatically switches to the public network connection and outputs the final connected network architecture as the first architecture data. Based on the set first time interval, it periodically detects the private network signal and switches the network architecture when necessary.

[0057] The identity authentication unit is used to collect the identity information and group information input by the user, wherein the identity information includes the user account, the intercom serial number and the integrated circuit card identification code, and input the identity information and group information into the user information database for verification. If the identity information and group information are located in the user information database, the verification is successful; if the identity information and group information are not located in the user information database, the verification fails and a verification failure signal is sent to the user end.

[0058] The identity authentication unit collects the account number, intercom serial number and integrated circuit card identification code entered by the user, and compares the collected identity information with the records in the user information database. If the information matches, the verification is successful and the user is allowed to continue the operation. If it does not match, a verification failure signal is sent to the user end to prevent the user from further operation.

[0059] The group joining unit is used to monitor the group call signal of the group corresponding to the group information in real time.

[0060] The group joining unit monitors the group call signal of the user-specified group to ensure that the user can receive group communication in time. Once the group call signal is detected, the device is prepared to participate in the group communication, such as adjusting the device status and preparing for voice transmission. The group call signal here is received by the PoC server and a multicast IP address is assigned. The PoC server broadcasts the multicast address to all online devices in the group and activates the RTP listener on the device side.

[0061] The terminal startup module is the core of the initialization and preparation of this system. It is responsible for the key tasks of device startup, network connection, user identity authentication and group joining, ensuring that the device can quickly and securely access the correct network and is ready for subsequent communication activities.

[0062] The group call initiating module includes a request sending unit, a resource allocation unit and a group call confirming unit.

[0063] The request sending unit is used to obtain the group call signal of the group call terminal and send it to the terminal starting module.

[0064] The request sending unit obtains the group call signal from the group call terminal and sends the group call signal to the terminal startup module for further processing

[0065] The resource allocation unit is used to establish a channel control mechanism, and the channel control mechanism is:

[0066] If the first architecture data is a private network, the private network base station is selected as the resource allocation channel.

[0067] If the first architecture data is a public network, a dynamic multicast address pool is created on the PoC server, wherein the multicast address pool includes a plurality of multicast addresses, and a unique multicast address is allocated to each online device in the group.

[0068] The resource allocation unit is provided with a heartbeat detection mechanism, which is:

[0069] If the online device has no voice data transmission within the preset second time interval, the multicast address corresponding to the online device is automatically released, and the released multicast address is returned to the multicast address pool.

[0070] The resource allocation unit establishes a channel control mechanism according to the first architecture data. If it is a private network, the private network base station is selected as the resource allocation channel with low latency and reliability. If it is a public network, a dynamic multicast address pool is created on the PoC server, and a unique multicast address is allocated to each online device. In addition, it also monitors whether the online device has voice data transmission within a preset second time interval. If there is no transmission, the corresponding multicast address is automatically released, and the released address is returned to the multicast address pool for reallocation.

[0071] The group call confirmation unit is used to receive a group call signal. When receiving the group call signal, the group call signal is sent to all online devices in the group to obtain voice data.

[0072] The group call confirmation unit receives the group call signal from the request sending unit, sends the group call signal to all online devices in the group, activates group communication, and starts to obtain voice data after the group call signal is confirmed for subsequent voice transmission.

[0073] The group call initiation module jointly ensures the smooth progress of group call communication, from signal initiation to resource allocation, to group call confirmation and voice data acquisition, forming a complete group call communication process. Through dynamic resource management and heartbeat detection mechanism, it can effectively manage communication resources and improve system efficiency and response speed.

[0074] The voice transmission module includes a multicast unit and a voice stream receiving unit.

[0075] The multicast unit is used to compress the voice data into Opus code and pack it into RTP data packets. The RTP data packets are marked with multicast addresses and the voice data are transmitted based on the PoC protocol.

[0076] The logic of transmission in the multicast unit is:

[0077] If the first architecture data is a private network, the RTP data packet is transmitted through the physical channel of the private network.

[0078] If the first architecture data is a public network, the RTP data packet is transmitted in the form of a multicast stream through the multicast address of the 4G / 5G IP multicast network.

[0079] The multicast unit compresses the voice data into Opus encoding, which is an efficient audio encoding format that can reduce the data size while maintaining the sound quality, and packages the compressed voice data into RTP packets, which is a protocol commonly used to transmit audio and video on the Internet. The multicast address is marked in the RTP packet to ensure that the data can be correctly sent to the intended recipient group. According to the PoC protocol, the voice data is transmitted by multicast or multicast. If the first architecture data is a private network, the RTP data packet is transmitted through the physical channel of the private network. If the first architecture data is a public network, the RTP data packet is transmitted in the form of a multicast stream through the multicast address of the 4G / 5G IP multicast network.

[0080] The voice stream receiving unit is used to start the online device to monitor the multicast address in real time, receive the voice data in the RTP data packet corresponding to the multicast address and play it.

[0081] The voice stream receiving unit starts the real-time monitoring of the multicast address by the online device to ensure that no RTP data packets transmitted to the multicast address are missed, receives the voice data in the RTP data packet corresponding to the multicast address, decodes and plays the received voice data, so that the user can hear the transmitted voice information.

[0082] The voice termination module includes a call termination unit and a framework release unit.

[0083] The call end unit is used to obtain the call end signal of the group call end, and the dispatch server sends the call end signal to the online device to stop the voice data transmission.

[0084] The call end unit monitors and obtains the call end signal sent by the group call end, sends the call end signal to all online devices through the dispatch server, and stops the transmission of voice data after receiving the call end signal, ending the current communication session.

[0085] The architecture release unit is used to obtain the first architecture data and release it. The logic of the release is:

[0086] If the first architecture data is a private network, the physical channel is released.

[0087] If the first architecture data is a public network, the multicast address of the 4G / 5G IP multicast network is released and the PoC multicast session is closed.

[0088] The group call is terminated after the architecture corresponding to the first architecture data is released.

[0089] The architecture release unit obtains the first architecture data, determines whether a private network or a public network is used, and if the first architecture data is a private network, releases the previously occupied physical channel; if the first architecture data is a public network, releases the multicast address of the 4G / 5G IP multicast network, and closes the PoC multicast session. After releasing the architecture resources corresponding to the first architecture data, the group call communication session is officially ended.

[0090] The public network transmission of the multicast unit caches the RTP data packets and uses forward error correction and retransmission mechanisms.

[0091] The multicast unit caches RTP packets so that it can retransmit lost packets when network conditions are poor. It uses forward error correction technology to detect and repair errors in the transmission process by adding redundant information to the packets. When packet loss or damage is detected, a retransmission mechanism is used to resend these packets to ensure data integrity and reliability.

[0092] The voice ending module ensures the release of resources and the termination of communication after the group call ends. The efficient operation and rational utilization of resources of the present invention are ensured through the transmission of the call ending signal, the release of network resources and the error correction and retransmission mechanism in the public network transmission.

[0093] The present invention uses multi-network fusion technology to preferentially connect to a private network, and automatically switches to a public network if the private network signal is insufficient, thereby achieving seamless switching and complementarity between the private network and the public network, and improving the reliability and stability of communication. This multi-network fusion communication scheduling method enables the system to automatically switch to the public network when the private network signal is insufficient, thereby ensuring the continuity and stability of communication, which is particularly important in the fields of emergency communication and public safety. The PoC protocol is adopted to achieve cluster communication based on a 4G wireless network. The PoC protocol enables terminal devices to perform cluster communication through a 4G / 5G network, supports functions such as group calls and single calls, and improves communication efficiency. The application of the PoC protocol enables the system to utilize existing cellular network resources to achieve wide coverage and fast communication connections, which has significant advantages in mobile scenarios and large-scale activities. The PoC solution adopts a specific optimized network transmission protocol, so that the traffic cost can be reduced by more than 80% compared with other PoC solutions, effectively reducing the communication cost. This is a huge boon for enterprises and groups that need to use intercom communication for a long time, and also makes the cluster communication system more economical and practical.

[0094] It should be understood by those skilled in the art that the embodiments of the present invention can be provided as methods, systems or computer program products. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program codes. Among them, the storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (Static Random Access Memory, referred to as SRAM), electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, referred to as EEPROM), erasable programmable read-only memory (Erasable Programmable Read Only Memory, referred to as EPROM), programmable read-only memory (Programmable Read-Only Memory, referred to as PROM), read-only memory (Read-Only Memory, referred to as ROM), magnetic memory, flash memory, disk or optical disk. These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0095] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A cluster communication system based on 4G wireless network, characterized in that: It includes a terminal startup module, a group call initiation module, a voice transmission module and a voice ending module; The terminal startup module is used to start the device and select the architecture for connection, output the first architecture data, collect the user identity information and group information input by the user and perform identity authentication, and monitor the group call signal of the group corresponding to the group information in real time; The group call initiation module is used to send a group call signal to the terminal start module, establish a channel control mechanism, and select a connection architecture according to the channel control mechanism. After receiving the group call signal, the terminal start module sends the group call signal to all online devices in the group to obtain voice data; The voice transmission module is used to compress the voice data, the voice data is marked with a multicast address, the voice data is transmitted based on the PoC protocol, the online device monitors the multicast address in real time, and plays the voice data corresponding to the multicast address after receiving it; The voice ending module is used to obtain a call ending signal, send the call ending signal to an online device, stop voice data transmission, release the architecture corresponding to the first architecture data, and end the group call.

2. A cluster communication system based on a 4G wireless network as claimed in claim 1, characterized in that: The terminal startup module includes an architecture connection unit, an identity authentication unit and a group joining unit; The architecture connection unit is used to start the device and set the architecture priority. The architecture priority is to connect to the private network first and obtain the private network signal. If the private network signal is less than the preset private network signal strength threshold, the public network is connected and the connected architecture is output as the first architecture data.

3. A cluster communication system based on a 4G wireless network as claimed in claim 2, characterized in that: The architecture connection unit is provided with an architecture switching time interval, which is a first time interval. The private network signal is detected based on the first time interval and the architecture switching is performed.

4. A cluster communication system based on a 4G wireless network as claimed in claim 3, characterized in that: The identity authentication unit is used to collect identity information and group information input by the user, the identity information includes the user account, the intercom serial number and the integrated circuit card identification code, and input the identity information and group information into the user information database for verification. If the identity information and group information are located in the user information database, the verification is successful. If the identity information and group information are not located in the user information database, the verification fails and a verification failure signal is sent to the user end; The group joining unit is used to monitor the group call signal of the group corresponding to the group information in real time.

5. A cluster communication system based on a 4G wireless network as claimed in claim 4, characterized in that: The group call initiation module includes a request sending unit, a resource allocation unit and a group call confirmation unit; The request sending unit is used to obtain the group call signal of the group call terminal and send it to the terminal starting module; The resource allocation unit is used to establish a channel control mechanism, and the channel control mechanism is: If the first architecture data is a private network, selecting a private network base station as a resource allocation channel; If the first architecture data is a public network, a dynamic multicast address pool is created on the PoC server, wherein the multicast address pool includes a plurality of multicast addresses, and a unique multicast address is allocated to each online device in the group; The group call confirmation unit is used to receive a group call signal, and when receiving the group call signal, sends the group call signal to all online devices in the group to obtain voice data.

6. A cluster communication system based on a 4G wireless network as claimed in claim 5, characterized in that: The resource allocation unit is provided with a heartbeat detection mechanism, and the heartbeat detection mechanism is: If the online device has no voice data transmission within the preset second time interval, the multicast address corresponding to the online device is automatically released, and the released multicast address is returned to the multicast address pool.

7. A cluster communication system based on a 4G wireless network as claimed in claim 6, characterized in that: The voice transmission module includes a multicast unit and a voice stream receiving unit; The multicast unit is used to compress the voice data into Opus code and pack it into RTP data packets, wherein the RTP data packets are marked with a multicast address, and the voice data is transmitted based on the PoC protocol; The voice stream receiving unit is used to start the online device to monitor the multicast address in real time, receive the voice data in the RTP data packet corresponding to the multicast address and play it.

8. A cluster communication system based on a 4G wireless network as claimed in claim 7, characterized in that: The logic of transmission in the multicast unit is: If the first architecture data is a private network, the RTP data packet is transmitted through the physical channel of the private network; If the first architecture data is a public network, the RTP data packet is transmitted in the form of a multicast stream through the multicast address of the 4G / 5G IP multicast network.

9. A cluster communication system based on a 4G wireless network as claimed in claim 8, characterized in that: The voice termination module includes a call termination unit and a framework release unit; The call end unit is used to obtain a call end signal from the group call end, and the dispatch server sends the call end signal to the online device to stop voice data transmission; The architecture release unit is used to obtain the first architecture data and release it. The logic of the release is: If the first architecture data is a private network, releasing the physical channel; If the first architecture data is a public network, the multicast address of the 4G / 5G IP multicast network is released and the PoC multicast session is closed; The group call is terminated after the architecture corresponding to the first architecture data is released.

10. A cluster communication system based on a 4G wireless network as claimed in claim 9, characterized in that: The public network transmission of the multicast unit caches the RTP data packets and uses forward error correction and retransmission mechanisms.

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